Implement power assertions (#1384)

This adds power assertions to Pkl!

This implements the SPICE described in
https://github.com/apple/pkl-evolution/pull/29

This follows the power assertions style of reporting also found in
Groovy, Kotlin, and others.

* Literal values are not emitted in the diagram
* Stdlib constructors of literals like `List(1, 2)` are also considered
  literals

Power assertions are added to:

* Failing type constraints
* Failing test facts

Power assertions are implemented as a truffle instrument to observe
execution.
When an assertion fails, the instrument is created and the assertion is
run again to observe facts.
This incurs runtime overhead to collect facts, but has no impact on code
in the non-error case.

---------

Co-authored-by: Islon Scherer <islonscherer@gmail.com>

docs/modules/release-notes/pages/0.31.adoc

@@ -20,7 +20,89 @@ To get started, follow xref:pkl-cli:index.adoc#installation[Installation].#
 
 News you don't want to miss.
 
-=== XXX
+=== Power Assertions
+
+Pkl's test output and error output has been improved with power assertions (https://github.com/apple/pkl/pull/1384[#1384])!
+
+Pkl has two places that are effectively assertions.
+These are:
+
+* Type constraint expressions
+* Test facts
+
+Currently, when these assertions fail, the error message prints the assertion's source section.
+However, this information can sometimes be lacking.
+It tells you what the mechanics of the assertion is, but doesn't tell you _why_ the assertion is failing.
+
+For example, here is the current error output of a failing typecheck.
+
+[source,text]
+----
+–– Pkl Error ––
+Type constraint `name.endsWith(lastName)` violated.
+Value: new Person { name = "Bub Johnson" }
+
+7 | passenger: Person(name.endsWith(lastName)) = new { name = "Bub Johnson" }
+----
+
+Just from this error message, we don't know what the last name is supposed to be.
+What is `name` supposed to end with?
+We just know it's some property called `lastName` but, we don't know what it _is_. 
+
+In Pkl 0.31, the error output becomes:
+
+[source,text]
+----
+–– Pkl Error ––
+Type constraint `name.endsWith(lastName)` violated.
+Value: new Person { name = "Bub Johnson" }
+
+    name.endsWith(lastName)
+    │    │        │
+    │    false    "Smith"
+    "Bub Johnson"
+
+7 | passenger: Person(name.endsWith(lastName)) = new { name = "Bub Johnson" }
+----
+
+Now, we know what the expecation actually is.
+
+This type of diagram is also added to test facts.
+When tests fail, Pkl emits a diagram of the expression, and the values produced.
+
+For example, given the following test:
+
+.math.pkl
+[source,pkl]
+----
+amends "pkl:test"
+
+facts {
+  local function add(a: Int, b: Int) = a * b
+  local function divide(a: Int, b: Int) = a % b
+  ["math"] {
+    add(3, 4) == 7
+    divide(8, 2) == 4
+  }
+}
+----
+
+The error output now includes a power assertion diagram, which helps explain why the test failed.
+
+[source,text]
+----
+module math
+  facts
+    ✘ math
+       add(3, 4) == 7 (math.pkl:9)
+       │         │
+       12        false
+       divide(8, 2) == 4 (math.pkl:10)
+       │            │
+       0            false
+
+0.0% tests pass [1/1 failed], 0.0% asserts pass [2/2 failed]
+----
 
 == Noteworthy [small]#🎶#